The following relates to the nuclear reactor arts, nuclear power generation arts, nuclear reactor control arts, nuclear reactor human-machine interface (HMI) arts, nuclear reactor control arts, and related arts.
The human-machine interface (HMI) and control systems of a nuclear power plant should be ergonomic to reduce likelihood of human operator error. These systems should also be designed to minimize likelihood of mechanical or electronic failure, and to be defensible against physical assault. While computer-based control systems have advantages, the use of computer systems is balanced against disadvantages including intangibility and the potential for malicious cyber-assault.
In existing nuclear power plants, these design constraints are accommodated by providing a control room for the nuclear power plant. An operator at the controls (OATC) deployed in the central control room is responsible for all aspects of operation of the nuclear island, which houses the nuclear reactor unit which includes the pressure vessel containing the nuclear reactor core comprising fissile material (e.g. 235U) immersed in primary coolant water and ancillary components such as a pressurizer, reactor coolant pumps (RCPs), and a control rod drive system including control rods operated by control rod drive mechanisms (CRDMS). In the case of a boiling water reactor (BWR), primary coolant is directly boiled to generate steam for operating the plant turbine. In a pressurized water reactor (PWR), primary coolant in liquid form flows through a steam generator to boil secondary coolant so as to generate the operating steam. The steam generator may be located external to the reactor unit, or inside the pressure vessel of the reactor unit (called an “integral PWR”). The nuclear reactor unit and external steam generator (if present) are housed in a radiological containment structure, usually made of steel or steel-reinforced concrete, and a reactor service building houses both the containment structure and the control room. Alternatively, the control room may be in a separate building located close to (e.g. adjacent) the reactor service building.
From the control room, the OATC has operational control of all safety and non-safety systems related to operating the nuclear reactor unit. These include (by way of illustrative example): reactor pressure and temperature control systems (e.g., CRDMs, pressurizer, et cetera); the emergency core cooling system; various water systems (e.g. component cooling water servicing pumps and other water-cooled components, circulating water servicing a condenser downstream of the turbine, a reactor coolant inventory/purification system); the steam turbine control system, the electrical generator control system, and electrical power distribution systems. Some of these components, such as the electrical generator, are not actually part of the nuclear island, but their operation is critical to safe operation of the nuclear island and hence are under control of the OATC.
Until recently, analog reactor control systems were predominantly used. Analog systems advantageously provide hard-wired connections and tangible switches, buttons, dials, annunciator lights, and other tangible user interface elements, and are impervious to cyber attack. The tangible nature of the analog control components facilitates diagnosis of any control system failure. The threat of malicious physical tampering is mitigated by locating the control room in the reactor service building with the nuclear reactor unit, which reduces cable run lengths. Digital, i.e. computer-based control systems are increasingly being used. In such cases, the digital communication systems are generally on an isolated digital data network (e.g., not connected with the Internet or to any local area network employed for general plant business operations, so as to mitigate the threat of cyber attack). The digital data network is typically a hard-wired network so as to enhance tangibility, although the use of wireless communication is contemplated. Some regulatory jurisdictions require an analog system backing up any digital control systems.
The nuclear power plant includes numerous other control systems that are unrelated to, or tangentially related to, safe operation of the nuclear island. These include, by way of illustrative example: electrical switchyard interfacing with the external power grid; utility system such as demineralized water (DW); water makeup systems; environmental monitoring; fire detection systems; and so forth. The impact of these systems on safe operation of the nuclear island is delayed or nonexistent. Some of these non-safety systems may be under control of the OATC inside the control room, while others may be under control of other plant personnel located elsewhere.
Overall coordination of plant operations is generally under the control of a Senior (or Supervisory) Reactor Operator (SRO), who provides on-site interfacing between the OATC, other plant operators, and entities outside the nuclear power plant (e.g., external electrical, water, and other utilities, the general public, and so forth). In this supervisory role, the SRO is typically located in a business-style office, and communicates with the OATC and other plant operators via telephone, although the SRO may be mobile and, for example, go to the control room when appropriate.
In the United States and most other jurisdictions, plant control is regulated, e.g. by the Nuclear Regulatory Commission (NRC) in the United States. In the NRC regulatory framework, the OATC and the SRO must be licensed by the NRC to operate the specific nuclear power plant at which they are employed. In practice, several OATCs, as well as the SRO, are required to be on-site at all times, and all licensed operators are required to partake in ongoing training including simulation time. The nuclear power plant must therefore employ several dozen OATCs in order to have sufficient capacity for full-time 24-hour operation.
Some nuclear power plants include two or more nuclear reactor units. In such cases, each nuclear power plant has its own control room with cabling between the control room and the controlled nuclear reactor unit, and each reactor unit is serviced by its own ancillary water, electrical, and other utility systems. Each reactor unit has its own SRO, and there may be a managing SRO overseeing all nuclear reactor units of the power plant.
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